harfbuzz: 1.7.5 -> 1.7.6

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/harfbuzz/versions.

These checks were done:

- built on NixOS
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 1.7.6 with grep in /nix/store/q29jj339iyq46gh6dx7zrpbgx07b7826-harfbuzz-1.7.6
- directory tree listing: https://gist.github.com/ea2a4f299a574853f5fa5137ff8505ca